Discrepancies in EPC ratings in a dwelling that was firstly assessed using a SAP method and then at a later date using an RdSAP method is a very common query among landlords and vendors.
The purpose of this post is to explain what the methodologies are and what causes the difference in the EPC ratings between SAP and RdSAP assessments.
There are two types of domestic energy assessments: SAP and RdSAP.
How can I see the type of assessment used for my dwelling?
You can see the type of assessment that was used to calculate the energy rating of your dwelling if you scroll down to the bottom of your EPC report and then look under “About this assessment”. The type of EPC assessment will be either SAP or RdSAP. If your property was built after 2008, it is very likely that your first EPC was a SAP Assessment. If that EPC has expired, then every subsequent EPC will be an RdSAP.
What is the SAP Assessment?
This is the type of assessment required for all new build properties, large extensions, or change of use building developments, i.e. turning a commercial building into flats. Usually, a developer, a builder or an architect are obliged to submit a SAP assessment. It is an assessment required as part of a Building Control application in order to prove that a proposed building meets the latest regulatory standards in terms of Dwelling Energy Rating (DER) and Dwelling Fabric Efficiency Rating (DFER). The assessment is prepared by a qualified SAP Assessor. This full data assessment methodology is based on using architectural specifications, especially for the u values of Walls, Floors, Roofs, Windows and Doors. Though no site survey is required, as the proposed dwelling may not yet exist, the process is more precise, and the calculations are far more expensive. If a dwelling meets the latest DER and DFER regulatory requirements, a SAP assessment produces higher EPC ratings. Under “Breakdown of property’s energy performance” one can see the detailed u values used for each thermal element, and if built as per the latest building standards these will rate as “good” or “very good”.
What is the RdSAP Assessment?
This is the type of assessment required for all existing dwellings. RdSAP was introduced by the Government for marketing purposes of such dwellings. Therefore, a real estate agent will insist that a vendor is required to make this assessment available to all prospective buyers. Likewise, a landlord is required by law to ensure that this assessment is available to all prospective tenants. Focusing on affordability rather than accuracy, this oversimplified energy rating assessment is prepared by a qualified Domestic Energy Assessor (DEA). This reduced data assessment methodology is based only on photographic evidence collected during a site survey. Though a site survey is required, the data collection process is non-intrusive and non-destructive. In essence, the DEAs will only photograph what is made available to them during a walk-through of the property, whether that is visible data, such as depth of external wall, or available paperwork, such as certificates of wall insulation provided by approved contractors.
During the RdSAP survey photographic evidence will be collected as and when possible. Consequently, the DEAs will not remove obstacles to access information. For example, DEAs will not push away furniture in order to access a window or a radiator. This means that if a dwelling meets the latest DER and DFER regulatory requirements, and no photographic evidence, or paper evidence, is made available to the DEA, then an RdSAP assessment will assume default values for all thermal elements, such as Walls, Floors, Roofs, and Windows. This may not reflect the actual build specifications. Under “Breakdown of property’s energy performance” one can see the description of such elements which, even in the case of a new dwelling, they may rate as “poor”. Inevitably, an RdSAP assessment may downgrade the EPC rating of a new dwelling.
Examples of SAP and RdSAP Assessments for the Same Dwelling
An example of a SAP assessment for a dwelling built in 2014 is shown here, where the dwelling rated B83.
When the above EPC expired, an RdSAP assessment was produced for the same dwelling 10 years later, and it is shown here, where the dwelling rated C80.
In the 2014 SAP Assessment, the assessor used architect-specified u values for the external walls of 0.18 W/m²K, producing a description of “very good” for the walls.
In the 2024 RdSAP Assessment, the DEA used default u values, producing a description of “good”, for the same walls.
In a similar way, there are discrepancies for all thermal elements, such as roof, floor and windows, where default u values were used instead of exact u values, producing an overall lower EPC rating.
RdSAP downgraded my EPC rating. What can I do?
If the difference between a current RdSAP result and a previous full SAP result is only a few points (i.e. from B to a C), then this is to be expected. There is no RdSAP assessment that will achieve full SAP results for the same dwelling.
You can request a full SAP Assessment provided that you have floor plans, sections, and elevations and detailed build specifications. However, if you are selling this dwelling your estate agent will not require SAP Calculations, as the lower cost RdSAP assessment meets law requirements for selling a house.
However, if proof of u value calculations are available for the Walls, Floors and Roof, as well as for the Windows, then the DEA can overwrite default u values which will result in a higher EPC rating.
For the Walls, Floors and Roof, the acceptable form of evidence is detailed u value calculations provided by an architect or by an accredited SAP Assessor.
For the Windows, the acceptable form of evidence is a letter from the windows’ manufacturer showing the u values of the windows, the address of the dwelling where the windows were fitted, the date the windows were fitted and full contact details of the supplier.
Conclusion
There are two different types of EPC Assessments: SAP for new build dwellings and RdSAP for existing dwellings. The RdSAP assessment is a simplified, less accurate methodology. Therefore, differences in EPC ratings may be produced between the two assessments.
You can ask a DEA to review data entered in RdSAP, such as to overwrite thermal element u values, provided that you can supply architectural specifications, and evidence of u value calculations, that will satisfy the Scheme’s minimum evidence requirements.
